"hl2.exe has stopped working" - Unable to load a map, GMod essentially completely broken

[lavacano]

1. Start GMod
2. Attempt to open gm_flatgrass (via console or via Start New Game, doesn't matter which)
3. Game gets to the "Initializing Game Data" stage, ULX has begun displaying the generic CSS MOTD
4. "hl2.exe has stopped working".

[url=https://dl.dropbox.com/u/5733962/ShareX/2013-01/hl2_153_crash_2013_1_26T4_5_43C0.mdmp]Here's my latest crashdump if anyone's got a viewer for it.[/url] I can't use dumps.garrysmod.com, Cloudflare keeps telling me it's unavailable.